Bacteria, viruses, coronavirus, fear or not?

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Bacteria are single-celled prokaryotic microorganisms, that means they do not have a true nucleus, mitochondria, or any other membrane-bound organelle like eukaryotes whose cells have a nucleus enclosed within membranes (and other membrane-bound organelles, e.g. mitochondria, Golgi apparatus). The number of bacteria on Earth exceed the number of all plants and animals, with an approximately 5×1030. In one gram of soil there are 40 million bacterial cells, and one million in a milliliter of fresh water.

In humans there are ~39 trillion bacteria, with 30% more than the number of human cells (in case of a 70 kg, 170 cm tall person.)  Most of them live in the gut flora and on the skin[1] and are harmless, some of them are beneficial, especially  those in the gut flora.

Several bacteria are pathogenic and cause infectious diseases, like the black plague caused by Yersinia pestis, Lyme-disease by Borelia burgdorferi or cholera by Vibrio cholerae.

Antibacterial drugs are used for the treatment of bacterial infections. This class of drug is considered as one of the biggest successes of medicinal chemistry. Penicillin saved countless lives in world war II. The first patient for septicemia was successfully cured on March 14, 1942.  For D-day 2.3 million of penicillin doses were prepared.


Figure 1: Advertisement for penicillin from Life magazine, August 1944 [3]

However nowadays we easily fell into exaggeration with the excessive use of antibiotics, that implies antibiotic resistance for several kind of bacteria.

Viruses on the other hand are they are self-reproducing chemical entities on the edge of living and lifeless. They are free forms of DNA or RNA that can’t reproduce on their own, they lack the enzyme systems needed for the genetic material reproduction. “They make more copies of themselves by hijacking the machinery of cells to replicate themselves”[4]. Their number is more than sum of the living organisms on Earth. Viruses can infect all type of life forms.

Viruses contain one type of single or double-stranded DNA or RNA, one of their classification is based on the type of their genetic material.

The scheme of viral replication can be seen in Figure 2. However, the processes are different in the case of DNA and RNA viruses (DNA viruses have to enter the nucleus for replication, RNA viruses can replicate in the cytoplasm).

Fighting against is with vaccines or antiviral drugs. Vaccines are mainly for immunization, thus for the prevention. Antivirals can interfere in several points of the viral replication. One major problem with the vaccines and the drugs is the high mutation rate of the viruses (especially of the RNA viruses, up to a million times higher than their hosts [5]).

viral replication1

Figure 2: Stages of viral replication

Now a few words about today’s the most feared virus: Coronavirus (Figure 3).

Coronaviruses contain a positive single-stranded RNA genome and a nucleocapsid (protein outer shell) with helical symmetry. The electron microscopic image of the virus looks like the virions have a halo or a crown, that is where their name comes from.


Figure 3: Structure and electron microscopic image of the coronaviral particles

This is not the first case in history that coronaviruses cause epidemic, for example in 2003 the severe acute respiratory syndrome (SARS) or the Middle East respiratory syndrome (MERS).

The novel coronavirus (2019-nCoV, SARS-CoV-2) infection is also a zoonosis, like the upper mentioned diseases (spreading between animals to humans). The epicenter of the viral infection is in Wuhan (Hubei province) in China. The origin of the virus is still unknown, some articles say that it is originated from bats, others from snakes. It is well-known that bats are the reservoir of several coronaviruses, so it is possible that the evolutional leap of the novel virus may have started from them.

Should we fear the SARS-CoV-2 ?

update: On the 8th of February WHO announced, that the disease caused by the novel coroanvirus will be referred to as COVID-19 (‘co’ and ‘vi’ stands for coroanvirus, ‘d’ for disease, and 19 indicated the year that is was first discovered).

Let’s compare it with the flu: According to the data from the CDC the flu this season caused approximately 19 million illnesses with 180.000 hospitalizations and 10.000 deaths. The fear of the novel coronavirus comes from several points, one of them is that we know very little (including the death rate, however it seems higher than the flu’s) of the SARS-CoV-2 because it is very new, compared to the flu. We know lot about the flu, because scientists have been studying it for decades, so we know what to expect, also the population learned to live with it.

Thanks to the Chinese scientists and authority the full genome of the SARS-Cov-2 virus is reported [6], thus several research groups have started developing a possible cure or vaccine.

Even cyclodextrins are involved in the fight against viruses. On this blog we reported several articles about cyclodextrins as antivirals. Also a few cyclodextrins can be as adjuvants for some antiviral drugs, for example as solubility enhancers, e.g. Gilead uses Sulfobutyl-ether-beta-cyclodextrin-enabled remdesivir. The company supplied remdesivir for 500 patients in China. Also, two clinical trials have been started in patients with moderate and sever coronaviral infections [7].

What do you think, should we fear it?


  1. Kiran, B., Reproduction in Bacteria. 2019: EDTECH.


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